When it comes to romantic relationships, women set the pace – literally.

That's the conclusion of researchers who studied walking speeds among a small group of heterosexual couples and their friends. They found that, as expected, men ambling solo generally walked faster than women – but that when men walked with their wives or girlfriends they slowed down to match their female partners' speeds. Women barely sped up at all.

"It's really men who do all the compromising," at least in this small aspect of romantic relationships, says Cara Wall-Scheffler, a biologist at Seattle Pacific University. She led the study published Wednesday online in the journal PLOS ONE.

For the study, Wall-Scheffler and colleagues invited 11 couples, along with some male and female friends of the pairs, to walk several times around a track solo and in various pairings. A total of 36 people ages 18 to 29 participated.

When walking alone, men traveled at 1.53 meters per second and women at 1.44 meters per second. That speed difference was expected because "men are taller and have longer legs," Wall-Scheffler says. But when walking with wives or girlfriends, holding hands or not, the guys slowed down.

As a biologist interested in evolution, Wall-Scheffler has a theory to explain this behavior: it has to do with males in roving hunter-gatherer groups not wanting to push women to walk too fast, lest the females over-exert themselves and harm their fertility.

But she says it also makes sense from an immediate psychological standpoint: Guys will slow down to "get that shoulder bumping, hip-bumping intimacy" with women they love.

It's worth noting that when guys were paired with female friends in the study, they did not slow down. When they walked with other guys, they actually sped up. And when women walked with female friends, both women slowed down, perhaps reflecting the intimacy of those relationships, Wall-Scheffler says.